Patent document 1 discloses an apparatus that detects raindrops adhering to a front windscreen of a vehicle by using a camera (capturing means) for detecting information surrounding the vehicle. In this apparatus, an area of a capturing frame is divided into an image area for detecting information surrounding the vehicle (capturing area image) and an image area for detecting raindrops (adhering matter observation image). For a process of detecting information surrounding a vehicle, captured image data of the image area for detecting the information surrounding the vehicle are used. For a process of detecting raindrops, captured image data of the image area for detecting raindrops are used. Furthermore, for the process of detecting raindrops, the captured image data are obtained by irradiating an adhering matter observation part in the front windscreen with an irradiation light from a dedicated light source.
In the apparatus disclosed in the Patent Document 1, for the captured image data used for the process of detecting information surrounding a vehicle, image data of a capturing frame captured with an exposure amount suitable for detecting information surrounding a vehicle are used, and for the captured image data used for the process of detecting raindrops, image data of a capturing frame captured with an exposure amount suitable for detecting raindrops are used. Specifically, following the rule that after capturing predetermined number of times consecutively the capturing frames for detecting information surrounding a vehicle with the exposure amount suitable for detecting the information surrounding the vehicle, the exposure amount is switched to the amount suitable for detecting raindrops and the capturing frame for detecting raindrops is captured only once; then the capturing processes are performed repeatedly. According to the above processes, high detection accuracies are ensured in both the process of detecting information surrounding a vehicle and the process of detecting raindrops.
Patent Document 1: Japanese Published Patent Application No. 2013-115625.